Intermittent fasting might be less effective in weight loss

It is no magic bullet for weight loss.


In recent years, intermittent fasting diets have gained increased popularity. Although, evidence about the effectiveness of fasting in comparison with traditional fasting is limited.

A new study from the team of physiologists at the University of Bath builds this evidence. The study suggests that intermittent fasting, such as the 5:2 diet, might be less effective than many people believe.

Thirty-six participants in their randomized control trial lost less weight when fasting than those following a traditional diet – even when their calorie intake was the same overall.

The participants were allocated into three groups:

Group 1 fasted on alternate days with their fast day, followed by eating 50% more than usual.

Group 2 reduced calories across all meals every day by 25%.

Group 3 fasted on alternate days (in the same way as Group 1) but followed their fast day with one day eating 100% more than usual.

Members across every group were devouring a typical diet of around 2000-2500 kcal each day on average during the beginning of the examination. However, throughout the three-week monitoring period, the two energy-restricted groups reduced this to 1500-2000 kcal overall. Furthermore, though groups 1 and 2 lowered their calorie intake by the same amount in an unexpected way, group 3’s diet saw them fast without diminishing overall calories.

Scientists found that group 2 lost 1.9 kg in just three weeks due to reduced body fat content. In comparison, group 1, who experienced the same reduced calorie intake by fasting on alternate days and eating 50% more on non-fasting days, lost almost as much body weight (1.6 kg).

However, only half this weight loss was from reduced body fat, with the remainder from muscle mass. Group 3, who fasted but increased their energy intake by 100% on non-fasting days, did not need to draw on their body’s fat stores for energy, and therefore weight loss was negligible.

Professor James Betts, Director of the Centre for Nutrition, Exercise & Metabolism at the University of Bath who led the research, explains“Many people believe that diets based on fasting are especially effective for weight loss or that these diets have particular metabolic health benefits even if you don’t lose weight.”

“But intermittent fasting for weight loss is no magic bullet, and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow.”

“Most significantly, if you are following a fasting diet, it is worth thinking about whether prolonged fasting periods are making it harder to maintain muscle mass and physical activity levels, which are known to be significant factors for long-term health.”

Journal Reference:
  1. Iain Templeman et al. A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults. DOI: 10.1126/scitranslmed.abd8034
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